Reduction of dehydroascorbate to ascorbate by the selenoenzyme thioredoxin reductase

Area of Science:

• Biochemistry
• Cell Biology
• Nutritional Science

Background:

• Ascorbate (vitamin C) recycling is vital for cellular health.
• The glutathione (GSH) system is the primary known pathway for dehydroascorbate reduction.
• The role of the selenium-dependent thioredoxin system in ascorbate regeneration was investigated.

Purpose of the Study:

• To determine if the thioredoxin system contributes to dehydroascorbate reduction and ascorbate regeneration.
• To assess the physiological significance of this pathway in vivo, particularly under selenium deficiency.

Main Methods:

• Purified rat liver thioredoxin reductase was assayed for dehydroascorbate reductase activity.
• The effect of purified thioredoxin on enzyme kinetics was evaluated.
• Dehydroascorbate reductase activity and ascorbate content were measured in liver cytosols from control and selenium-deficient rats.

Main Results:

• Purified thioredoxin reductase demonstrated NADPH-dependent dehydroascorbate reductase activity.
• Thioredoxin reductase activity was enhanced by the addition of thioredoxin.
• Selenium deficiency significantly reduced liver thioredoxin reductase activity, dehydroascorbate reductase activity, and ascorbate content.

Conclusions:

• The selenium-dependent thioredoxin system is capable of reducing dehydroascorbate.
• This thioredoxin system-mediated reduction plays a significant role in maintaining liver ascorbate levels.
• The findings highlight a novel pathway for vitamin C regeneration crucial for cellular homeostasis.